GHG Inventory Verification

Verification standards — ISO 14064-3 and ISAE 3410

Two standards dominate GHG inventory verification:

ISO 14064-3 (Specification with guidance for the verification and validation of greenhouse gas statements): The international standard specifically designed for GHG verification. Provides requirements for verification bodies and verification procedures. Used by specialist environmental verification firms (Bureau Veritas, SGS, DNV, LRQA) for standalone GHG audits.

ISAE 3410 (Assurance engagements on greenhouse gas statements): The accounting profession's standard for GHG assurance — used by audit firms (Big Four and national firms) for GHG assurance as part of broader sustainability assurance engagements. ISAE 3410 is the standard most commonly used for CSRD limited assurance of GHG disclosures.

Both standards cover the same substantive requirements — independence, competence, planning, evidence gathering, and reporting. The difference is professional context: ISO 14064-3 is the engineering/environmental standard; ISAE 3410 is the accounting standard. Under CSRD, either is acceptable.

AA1000AS v3: The AccountAbility standard is broader than GHG-specific — it covers the full sustainability report. Where CSRD assurance is provided under AA1000AS, GHG data is assessed as part of the overall report assurance rather than as a standalone GHG audit.

What verifiers check — the evidence requirements

A GHG verification engagement typically follows these steps:

Planning: Review of the GHG inventory methodology, materiality thresholds, organisational boundary, and prior year audit findings. Assessment of risk areas — high-emission sources, complex calculations, new data sources.

Data testing: Sample-based testing of activity data against source records — fuel invoices, utility bills, fleet fuel cards, waste transfer notes. For the sampled data points, the verifier traces from the source document through to the reported emission figure.

Calculation review: Verification that emission factors used are appropriate, correctly sourced, and from the right reporting year. GWP values checked against IPCC AR6. Scope boundary assessment — are all material sources included?

Scope 3 assessment: For Scope 3, verifiers assess: completeness of category screening, materiality of excluded categories, appropriateness of calculation methods, and consistency with prior year. Scope 3 verification applies higher uncertainty tolerances than Scope 1 and 2 — typically ±10% for activity-based categories and ±30% for spend-based categories.

Conclusion: Limited assurance conclusion states that nothing has come to the verifier's attention to indicate the GHG inventory is materially misstated. Reasonable assurance conclusion positively states the inventory is fairly presented.

Preparing for GHG verification — the documentation requirement

The most common GHG verification finding is inadequate documentation — the emission figure is plausible but the trail from source data to reported figure is unclear or incomplete.

For each emission source in your inventory, maintain:

Source document: the original invoice, meter reading, fuel card statement, or other primary record showing activity data (volume, quantity, kWh).

Calculation workbook: the spreadsheet or system showing activity data × emission factor = kg CO2e, with the factor source and version identified.

Boundary evidence: documentation confirming which entities and sources are within scope — and which are excluded and why.

Methodology note: a written description of your inventory approach — boundary, base year, calculation methods, factor sources, and any estimations or assumptions made.

For Scope 3: supplier data requests and responses; EEIO factor sources; spend data extraction from procurement systems; calculation workbooks for each category.

Build documentation into your data collection process throughout the year — do not reconstruct it retrospectively for the verification engagement. ESGMaster maintains automated audit trails for every calculation, significantly reducing verification preparation time.

Frequently asked questions